The present invention relates to an optical information recording medium and an optical information recording/reproducing apparatus in which information is optically recorded, and more particularly to an optical information recording medium and an optical information recording/reproducing apparatus suitable for recording/reproduction of data based on information of pits preliminarily provided on a disk.
In recent years, a so-called optical disk system in which information is optically recorded in and reproduced from a disk-like recording medium has been developed. One format for such an optical disk system is known as the sampled format. The details of the sampled format system are discussed in the proceedings of SPIE, Vol. 695, Optical Mass Data Storage II, 1986, pp. 112-115 and pp. 239-242.
In the sampled format system, a tracking error signal and a timing signal are obtained by use of sample marks which are preliminarily provided on a disk, as shown in FIG. 1. The timing signal is multiplied to extract a clock signal and the detection of a servo system error signal such as a tracking error signal or a focusing error signal and the recording/reproduction of data is made in synchronism with the extracted clock signal. The sample marks include pairs of wobbling pits 7-1 and 8-1, 7-2 and 8-2, - - - , and 7-n and 8-n positioned at a distance of 1/4 track pitch from virtual track centers 6-1, 6-2, - - - and 6-n in opposite directions and timing pits 9-1, 9-2, - - - , 9-n positioned on the track centers. For example, a tracking error signal is detected from a difference in amplitude between signals reproduced from the wobbling pits 7-1 and 8-1 and a clock signal is extracted from the timing pit 9-1. A so-called singular pattern is employed in which no modulation pattern is present between the pits 8-1 and 9-1 (or eighteen 0's are continuously present), which allows the discrimination of the sample mark. The positions of the first wobbling pits 7-1 to 7-n change for every 16 tracks in order to obtain a cross-track signal.
A data format is shown in FIG. 2. One track or one track turn is divided into 32 sectors, each sector is composed of 43 segments and each segment is divided into 18 bytes. Each byte is divided into 15 channel bits. One of the 43 segments is provided for sector indentification information (ID) and contains sector identification information which is recorded in the form of a pre-pit. Data is recorded in the 42 remaining segments. Since one segment is constructed by a sample mark of 2 bytes and a data region of 16 bytes, data of 672 bytes is recorded in one sector. The 672-bytes of data include 512-bytes of user data, 16-bytes of control data and 144-bytes of error correction code.
When recording is to be made, data is recorded in the data region between the sample marks in such a manner that 8 bits of data or one byte is converted in-to 15 channel bits (=1 symbol) in accordance with a modulation system called 4/15 modulation. The 4/15 modulation is described in the above-mentioned article of the proceedings of SPIE. In the 4/15 modulation, the 15th channel bit is always "0" and two odd-numbered channel bits and two even-numbered channel bits of the fourteen remaining channel bits are "1". A "1" may continue up to a maximum of four successive bits but the number of "0"'s which may occur between "1" and "1" is a maximum of two. (Though only one "0" may appear between "1" and "1" in a portion over adjacent bytes in the data region, no problem arises since this "0" is "0" alloted to the 15th channel bit.) A "0" may continue up to a maximum of seventeen successive bits. (For example, this corresponds to the case of data of 00, EE in a hexadecimal notation in which the 1st, 2nd, 5th and 6th channel bits of the first data and the 9th, 10th, 13th and 14th channel bits of the second data are "1" and the remaining bits are "0".)
When data is to be reproduced, the amplitude of a reproduced signal for each channel bit is detected to select the uppermost and next uppermost ones of the reproduced signal amplitudes for the odd-numbered channel bits and the even-numbered channel bits, respectively and it is judged that a pit or "1" exists at each of the bit positions having the two uppermost amplitudes. Data is determined or reproduced by referring to a conversion table for demodulation of 4/15 modulation.
A recording area of the disk has an inner diameter of 60 mm and an outer diameter of 120 mm, the track density is 1.5 .mu.m/track, the line or track recording density is 0.95 .mu.m/bit and the speed of rotation of the disk is usually 1800 r.p.m. though not limited to these values. The number of sample marks per one track turn is 1376 and the smpling frequency is about 41 kHz.
In this system, since a tracking servo is performed by use of only information from the sample marks, the amount of track movement when access is made is also derived from the sample marks. Since the positions of the first wobbling pits 7-1 to 7-n change for every 16 tracks, as shown in FIG. 1, the track movement amount for every 16 tracks can be detected by detecting the first wobbling bit positions.
The detection limit of the speed of movement of a pickup by pickup driving means upon access is about 1 m/s.